The dress was designed in 1986 for the then Princess of Wales' to wear during a royal visit to Austria, and the stylish royal wore it a number of times afterwards.
Diana originally sold the dress at her infamous auction at Christie's in New York in 1997 – which was just three months before she died.
It was then sold again in 2013 by Kerry Taylor Auctions for $182,000.
The second outfit up for sale is an Emanuel couture wool day dress, the same designer who made her iconic wedding dress.
The dress was worn by Diana on a 1985 trip to Venice and auctioneers are hoping it will sell for as much as $30,000.